Crystal form of N-(4-trifluoromethylphenyl)-5-methylisoxazole-4-carboxamide

ABSTRACT

The invention relates to a crystal modification of the compound of the formula Iand the processes for the preparation of and use that crystal modifications 1. The invention is used for treating acute immunological episodes, such as sepsis, allergies, graft-versus-host and host-versus-graft-reactions, autoimmune diseases, in particular rheumatoid arthritis, systemic lupus erythematosus, multiple sclerosis, psoriasis, atopic dermatitis, asthma, urticaria, rhinitis, uveitis, type 11 diabetes, liver fibrosis, cystic fibrosis, colitis, cancers, such as lung cancer, leukemia, ovarian cancer, sarcomas, Kaposi&#39;s sarcoma, meningioma, intestinal cancer, lymphatic cancer, brain tumors, breast cancer, pancreatic cancer, prostate cancer, or skin cancer.

This Appln is a Div of Ser. No. 09/428,499 Oct. 28, 1999 U.S. Pat. No.6,221,891 which is a div of Ser. No. 09/129,783 Aug. 6, 1998 U.S. Pat.No. 6,060 494.

This case claims benefit under 35 U.S.C. §119 of German prioritydocument 19734438.0 filed on Aug. 8, 1997. This document, as well asGerman priority document 19756093.8, filed Dec. 17, 1997, are herebyincorporated by reference.

The invention relates to a novel readily soluble crystal modification(hereafter referred to as “the first crystal modification”) of thecompound of formula I

in which the transmission X-ray diffraction pattern obtained with afocusing Debye-Scherrer beam and Cu—K_(α1)-radiation, has lines at thefollowing diffraction angles 2θ:

Lines of strong intensity: 10.65; 14.20; 14.80; 16.10; 21.70; 23.15;24.40; 24.85; 25.50:; 25.85; 26.90; and 29.85 degrees,

Lines of medium intensity: 7.40; 9.80; 13.10; 15.45; 16.80; 20.70;21.45; 22.80; 23.85; 27.25; and 28.95 degrees,

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is the X-ray diffraction pattern of the first crystalmodification.

FIG. 2 is the X-ray diffraction pattern of the second crystalmodification.

FIG. 3 is the infrared spectrum of the first crystal modification.

The X-ray diffraction pattern of the first crystal modification recordedusing Cu—K_(α1) radiation is shown in FIG. 1. The pattern was recordedusing the STADI P two-circle diffractometer from Stoe (Darmstadt,Germany) and the computer-assisted single crystal diffractometer R3 mNfrom Siemens (radiation used: MoK_(α)).

The infrared spectrum of the first crystal modification of the compoundof formula I (1 mg in 300 mg of KBr) recorded using an infraredspectrophotometer shows the following main bands (units: cm⁻¹):

1321 1481 672 3201 1607 3355 763 701 1109 1264 908 948 1065 1384 754 5111536 1361 592 733 1663 852 427 960 1241 1014 3111 1779 1410 3297 30651811 1160 877 3221 484 1691 940 974 3442 831 3274 3129 3434 1188 894 628

The stated wavenumbers are arranged in ascending intensity. The infraredspectrum of the first crystal modification of the compound of formula Iaccording to Example 1 is shown in FIG. 3, the transmittance in % beingstated along the ordinate and the wavenumber in cm⁻¹ along the abscissa.

The compound of formula I crystallizes in the first crystal modificationin the space group P2₁/c with 8 molecules in the unit cell. Molecules ofthe compound of formula I are present as dimers which originate from theindividual molecules by formation of a —C═O . . . HN hydrogen bridgebond (2.938 Å), the two molecular levels being virually perpendicular toone another (91.2°). The two molecules have very differentconformations. The angles made by the five- and six-membered rings withthe central carbonyl group are 5.4° and 2.1° and 23.4° and 23.1 °,respectively. The latter twist creates the steric preconditionspermitting the hydrogen bridge bond between the two molecules.

The compound of formula I is known per se and is also referred to asLeflunomide (HWA 486). It can be obtained in the manner described inU.S. Pat. No. 4,284,786. However, the crystals prepared byrecrystallization from, for example, toluene are obtained in a crystalform called the second crystal modification. The X-ray diffractionpattern (Cu—K_(α1) radiation) of the second crystal modification isshown in FIG. 2 and has characteristic lines at the followingdiffraction angles 2θ:

Lines of strong intensity: 16.70; 18.90; 23.00; 23.65; and 29.05degrees.

Lines of medium intensity: 8.35; 12.65; 15.00; 15.30; 18.35; 21.25;22.15; 24.10; 24.65; 25.45; 26.65; 27.40; 28.00; and 28.30 degrees.

The compound of formula I crystallizes in the second crystalmodification in the space group P2₁/c with 4 molecules in the unit cell.The molecule is essentially planar. The angle between the planar groupsof atoms is less than 2.4°. The molecules are arranged in stacks in thecrystal. The molecules lie in stacks adjacent to one another and arearranged in an antiparallel manner. Very weak hydrogen bridge bonds linkthe dimers in the crystal (NH . . . N: 3.1444 Å). The C═O group is notinvolved in any hydrogen bridge bonding.

The X-ray diffraction patterns furthermore permit the determination ofthe amount of the first crystal modification in a mixture containingboth modifications. The line at 2θ=8.35° of the second crystalmodification and the line at 20=16.1° of the first crystal modificationare suitable for the quantitative determination. If the ratio of thepeak heights is calculated and is correlated with the content of themodification, a calibration line is obtained. The limit of detection ofthis method is about 0.3% of the first crystal modification in crystalscontaining the second crystal modification.

The first crystal modification has better water solubility than thesecond crystal modification. At 37° C., 38 mg/l of the first crystalmodification can be dissolved whereas 25 mg/l of the second crystalmodification go into solution. Furthermore, the first crystalmodification is stable in the temperature range from −15° C. to +40° C.,preferably from 20° C. to 40° C., and is not converted into the secondcrystal modification under these conditions.

The first crystal modification, according to the invention, of thecompound of formula I is obtained, for example, by heating a suspensionof crystals of the second crystal modification or mixtures of the secondcrystal modification and the first crystal modification of the compoundof formula I in a solvent to a temperature of from about 10° C. to about40° C., preferably from about 15° C. to about 30° C., in particular fromabout 20° C. to about 25° C. The preparation rate is essentiallydependent on the temperature. Solvents in which the compound of formulaI are poorly soluble are advantageously used. For example, it ispossible to use water or aqueous solutions containing (C₁-C₄) alcohols(e.g., methanol, ethanol, propanol, isopropanol, butanol or isobutanol)and/or ketones, such as acetone or methyl ethyl ketone, or mixturesthereof. As a rule, the heating is carried out in aqueous suspension,expediently while stirring or shaking. The heat treatment is carried outuntil through this process the second crystal modification is completelyconverted into the first crystal modification.

The complete conversion of the second crystal modification to the firstcrystal modification is dependent on the temperature and, as a rule,takes from 36 hours to 65 hours, preferably from 48 hours to 60 hours,at a temperature of 20° C. The reaction is monitored by X-raydiffraction or I!R spectroscopy by means of samples taken during thetreatment.

A further process for the preparation of the first crystal modificationof the compound of formula I comprises dissolving the second crystalmodification or mixtures of the first and second crystal modificationsin a solvent and then cooling the solution abruptly to temperatures offrom about −5° C. to about −25° C. The terms “solution” and “suspension”are used interchangeably throughout and are meant to includecircumstances where a solid or solids is placed in a solvent or amixture of solvents regardless of solubility. Suitable solvents are, forexample, water-miscible solvents such as (C₁-C₄) alcohols, as well asketones, such as acetone or methyl ethyl ketone, or other solvents, suchas ethyl acetate, toluene dichloromethane or mixtures thereof. Thedissolution process takes place at room temperature of from about 20° C.to about 25° C. or at elevated temperatures up to the boiling point ofthe solvent under atmospheric pressure or under superatmospheric orreduced pressure. The solution obtained is, if required, filtered inorder to separate off undissolved components or crystals fromLeflunomide. The filtered solution is then cooled so rapidly that onlycrystals of the first crystal modification form. An adequate coolingprocess comprises, for example, introducing the filtered solution into avessel which has been cooled to −15° C. or spraying filtered solutioninto a space cooled to −10° C. or cooling the solution under vacuumcondensation conditions.

The preferred process comprises introducing the compound of formula Iinto methanol and carrying out the dissolution process at the boilingpoint of methanol at atmospheric pressure or reduced pressure, thenfiltering the hot solution and transferring the filtered solution to avessel which has been cooled to −15° C., the transfer being effected soslowly that the temperature of the crystal suspension obtained does notincrease to more than −10° C. The precipitated crystals are then washedseveral times with methanol and are dried under reduced pressure.

The crystallization can be carried out without seeding with crystals ofthe first crystal modification; however seeding with crystals of thefirst crystal modification is the preferred method. The seeding iseffected in the cooled vessel. The amount of seed material depends onthe amount of the solution and can be easily determined by a person ofordinary skill in the art.: The aforementioned processes are alsosuitable for converting mixtures containing the first and second crystalmodifications into an essentially pure the first crystal modification ofthe compound of formula I.

The invention also relates to novel processes for the preparation of thesecond crystal modification of formula I. By means of novel processes,it is also possible to convert mixtures containing the first and secondcrystal modifications specifically into the second crystal modification.For this purpose, for example, crystals of the first crystalmodification, or mixtures of the first and second crystal modificationsare dissolved in a solvent. Suitable solvents are, for example,water-miscible solvents such as C₁-C₄ alcohols (e.g., methanol, ethanol,propanol, isopropanol, butanol or isobutanol), as well as ketones suchas acetone or methyl ethyl ketone, or mixtures thereof. Mixtures oforganic solvents with water, for example of about 40% to about 90% ofisopropanol, have also proven useful.

The dissolution process is preferably carried out at elevatedtemperature up to the boiling point of the respective solvent. The hotsolution is kept at the boiling point for some time in order to ensurecomplete dissolution of the compound of formula I. The filtered solutionis then cooled so slowly that only crystals of the second crystalmodification form. Cooling is preferably effected to final temperaturesof about 20° C. to about −10° C., in particular to temperatures of about10° C. to about −50° C., very particularly preferably to temperatures offrom about 10° C. to about 5° C. The crystals are separated off andwashed with isopropanol and then with water. The substance is dried atelevated temperature, preferably at about 60° C. under reduced pressureor at atmospheric pressure.

A preferred process for preparing the second crystal modificationcomprises dissolving the compound of formula I in an about 80% strengthisopropanol at the boiling point of isopropanol and at atmosphericpressure or under reduced pressure and then cooling the hot solution soslowly that the crystallization takes place at temperatures of more thanabout 40° C., preferably from about 40° C. to about 85° C., particularlypreferably from about 45° C. to about 80° C., in particular from about50° C. to about 70° C. The precipitated crystals are then washed severaltimes with isopropanol and are dried under reduced pressure. Thecrystallization can be carried out without seeding with crystals of thesecond crystal modification or preferably in the presence of crystals ofthe second crystal modification, which are introduced by seeding intothe solution containing the compound of formula I. Seeding may also becarried out several times at different temperatures. The amount of theseed material depends on the amount of the solution and can be readilydetermined by a person of ordinary skill in the art.

A particularly preferred process for the preparation of the compound offormula I in the second crystal modification comprises

a) transferring the compound of formula I where no the second crystalmodification is present or mixtures of the second crystal modificationand other crystal forms of the compound of formula I into an organicsolvent or into mixtures of organic solvents and water,

b) heating the mixture obtained to a temperature greater than about 40°C. to about the boiling point of the organic solvent,

c) diluting the resulting solution with water or distilling off organicsolvent so that the organic solvent and the water are present in a ratioof from 4:1 to 0.3:1 and

d) carrying out the crystallization at temperatures above about 40° C.(The solution obtained is preferably filtered after process step b).

By means of the particularly preferred process, it is also possible toconvert mixtures containing the first and second crystal modificationsspecifically into the second crystal modification. For this purpose,crystals of the first crystal modification or mixtures of the first andsecond crystal modifications are dissolved in a mixture containingorganic solvents and water. Suitable solvents are, for example,water-miscible solvents such as C₁-C₄ alcohols (e.g., methanol, ethanol,propanol, isopropanol, butanol or isobutanol), as well as ketones suchas acetone or methyl ethyl ketone, or mixtures thereof.

Advantageous mixtures contain organic solvent and water in a ratio offrom about 1:1 to about 8:1, preferably from about 2:1 to about 6:1, andin particular from about 3:1 to about 5:1.

The preparation of the solution is preferably carried out at elevatedtemperature, in particular at temperatures of from about 41° C. to theboiling point of the respective organic solvent. The heated solution is,for example, kept for some time at the boiling point in order to ensurecomplete dissolution of the compound of formula I. The dissolutionprocess can also be carried out at superatmospheric pressure. Thesolution is then filtered. The filter used has a pore diameter of fromabout 0.1 μm to about 200 μm. Advantageously, water which has the sametemperature as the filtered solution is then added to the filteredsolution, or the organic solvent is distilled off. The solutionsobtained advantageously contain the organic solvent and water in a ratioof from about 4:1 to about 0.3:1, preferably from about 2:1 to about0.6:1, particularly preferably from about 1.6:1 to about 0.8:1. Coolingis then carried out slowly to a minimum temperature of about 40° C. andcrystals form. The crystals are separated off and are washed withisopropanol and then with water and, advantageously, dried at elevatedtemperature, preferably at about 60° C., under reduced pressure or atatmospheric pressure.

A particularly preferred process comprises dissolving the compound offormula I in a mixture of isopropanol and water in a ratio of from about4:1 to about 5:1 and at the boiling point of isopropanol underatmospheric pressure or reduced pressure and filtering the solutionpreferably, a filter pore of lumen diameter is used. Thereafter, waterat the same temperature is added to the hot solution in an amount suchthat a ratio of isopropanol to water is from about 2:1 to about 0.8:1.The crystallization is then carried out at temperatures of more thanabout 40° C., preferably from about 40° C. to about 85° C., particularlypreferably from about 45° C. to about 80° C., in particular from about50° C. to about 70° C. The crystals are then washed several times withisopropanol and are dried under reduced pressure.

A further process for the preparation of the second crystal modificationfrom the first crystal modification or from a mixture containing thefirst and second crystal modifications comprises heating the solid formsto a temperature of from above about 40° C. to about 130° C., preferablyfrom about 50° C. to about 110° C., in particular from about 70° C. toabout 105° C., very particularly preferably about 100° C. The conversionof the first crystal modification into 1 is dependent on the temperatureand, for example at about 100° C., takes from 2 to 5 hours, preferablyfrom 2 to 3 hours.

A further process for the preparation of the second crystal modificationcomprises preparing a suspension containing crystals of the firstcrystal modification or a mixture of crystals containing the first andsecond crystal modifications and a solvent.

The second crystal modification of the compound of formula I is obtainedby heating the suspension of the crystals in a solvent to a temperatureof more than about 40° C., preferably from about 41° C. to about 100°C., in particular from about 50° C. to about 70° C. The preparation isessentially dependent on temperature. Advantageous solvents are those inwhich the compound of formula I has poor solubility. For example, it ispossible to use water or aqueous solutions containing C₁-C₄ alcohols,ketones, such as methyl ethyl ketone or acetone, or a mixture thereof.As a rule, the heating is effected in an aqueous suspension, expedientlywhile stirring or shaking. The heat treatment is carried out until thefirst crystal modification has been significantly converted into thesecond crystal modification.

The conversion of the first crystal modification into the second crystalmodification is dependent on the temperature and, as a rule, takes from20 hours to 28 hours, preferably 24 hours, at a temperature of 50° C.The reaction is monitored by X-ray diffraction or IR spectroscopy bymeans of samples taken during the treatment.

The first crystal modification, according to the invention, of thecompound of formula I is suitable, for example, for the treatment of

acute immunological episodes, such as sepsis, allergies,graft-versus-host- and host-versus-graft-reactions

autoimmune diseases, in particular rheumatoid arthritis, systemic lupuserythematosus, multiple sclerosis

psoriasis, atopic dermatitis, asthma, urticaria, rhinitis, uveitis

type II diabetes

liver fibrosis, cystic fibrosis, colitis

cancers, such as lung cancer, leukemia, ovarian cancer, sarcomas,Kaposi's sarcoma, meningioma, intestinal cancer, lymphatic cancer, braintumors, breast cancer, pancreatic cancer, prostate cancer or skincancer.

The invention also relates to drugs comprising an effective content ofthe first crystal modification of the compound of formula I togetherwith a pharmaceutical excipient, additive and/or additional activeingredients and adjuvants.

The drugs according to the invention, comprising an effective content ofthe first crystal modification of the compound of formula I, have thesame efficacy in humans who suffer from rheumatic arthritis incomparison with the treatment with a drug comprising an effectivecontent of the second crystal modification of the compound of formula I.

The invention furthermore relates to a process for the preparation ofthe drug, which comprises processing the first crystal modification ofthe compound of formula I and a pharmaceutical excipient to give apharmaceutical dosage form.

The drug according to the invention may be present as a dosage unit indosage forms such as capsules (including microcapsules), tablets(including sugar-coated tablets, pills) or suppositories, the capsulematerial performing the function of the excipient where capsules areused and it being possible for the content to be present, for example,as a powder, gel, emulsion, dispersion or suspension. However, it isparticularly advantageous and simple to prepare oral (peroral)formulations containing the first crystal modification of the compoundof formula I, which contain the calculated amount of the activeingredient together with a pharmaceutical excipient. An appropriateformulation (suppository) for rectal therapy may also be used.Transdermal application in the form of ointments or creams or oraladministration of tablets or suspensions which contain the formulationaccording to the invention is also possible.

In addition to the active ingredients, ointments, pastes, creams, andpowders may contain conventional excipients, for example, animal andvegetable fats, waxes, paraffins, starch, tragacanth, cellulosederivatives, polyethylene glycols, silicones, bentonites, talc, zincoxide, lactose, silica, aluminum hydroxide, calcium silicate, polyamidepowder, or a mixture of these substances.

The tablets, pills or granules can be prepared by conventionalprocesses, such as compression, immersion, or fluidized-bed processes,or by coating in a pan, and contain excipients and other conventionaladjuvants, such as gelatine, agarose, starch (for example potato, cornor wheat starch) cellulose, such as ethyl cellulose, silica, varioussugars, such as lactose, magnesium carbonate and/or calcium phosphates.The sugar-coating solution usually comprises sugar and/or starch syrupand generally also contains gelatine, gum Arabic, polyvinylpyrrolidone,synthetic cellulose esters, surfactants, plasticizers, pigments, andsimilar additives according to the prior art. Any conventional flowregulators, lubricants, such as magnesium stearate, and externallubricants may be used for the preparation of the formulations.

The dosage to be used is of course dependent on various factors, such asthe host be treated (i.e., human or animal), age, weight, general stateof health, the severity of the symptoms, the disease to be treated, thetype of accompanying treatment with other drugs, or the frequency of thetreatment. The doses are administered in general several times per dayand preferably once to three times per day.

A suitable therapy therefore comprises, for example, administering one,two or 3 single doses of a formulation containingN-(4-trifluoromethylphenyl)-5-methylisoxazole-4-carboxamide in The firstcrystal modification in an amount of from 2 to 150 mg, preferably from10 to 100 mg, in particular from 10 to 50 mg.

The amount of the active ingredients does of course depend on the numberof single doses and also on the disease to be treated. The single dosemay also comprise a plurality of simultaneously administered dosageunits.

EXAMPLE 1 Preparation of the First Crystal Modification

About 40 mg of the compound of formula I, prepared according to U.S.Pat. No. 4,284,786, were shaken with 40 ml of water in bottles (volume45 ml). The shaking of the closed bottles was carried out at 15° C.-25°C. in a water bath. After 48 hours, a sample was taken, filtered anddried and a powder X-ray diffraction pattern was prepared. Themeasurement was carried out using the STADI P two-circle diffractometerfrom Stoe (Darmstadt, Germany) with Cu—K_(α1) radiation by theDebye-Scherrer method under transmission conditions.

FIG. 1 shows the resulting X-ray diffraction pattern and is typical ofthe first crystal modification of the compound of formula I.

EXAMPLE 2 Solubility in Water

Apparatus flask, magnetic stirrer, water bath 37° C. ± 0.5° C. Mediumwater (+37° C.) Sampling 5 hours Preparation First and second crystalmodifications according to Examples 1 and 2 were transferred to waterand stirred vigorously at 37° C. Detection UV spectroscopy at awavelength of 258 μm

Result:

Second crystal modification 25 mg dissolved in 1 liter of water at 37°C. First crystal modiflcation 38 mg dissolved in 1 liter of water at 37°C.

EXAMPLE 3 Stability of the First Crystal Modification

Samples of The first crystal modification were prepared as in Example 1and were stored at various temperatures at atmospheric humidity. Afterthe stated times, samples were taken and an X-ray diffraction patternwas prepared as in Example 1. Table 1 shows the results.

TABLE 1 Time (Months) Storage conditions Crystal modification 1 −15° C.First 3 −15° C. First 6 −15° C. First 1 +25° C. First 3 +25° C. First 6+25° C. First 1 +40° C. First 3 +40° C. First 6 +40° C. First 1 +40°C./75% relative humidity First 3 +40° C./75% relative humidity First 6+40° C./75% relative humidity First 1 +60° C. about 76% Second 3 +60° C.Second ¹⁾A calibration curve was used for the determination of thesecond crystal modification.

For preparing the calibration curve for the quantitative determination,the reflection at 2θ=8.35° was used for phase 1 and the reflection at2θ=16.1° was used for phase 2. The ratios of the corresponding peakheights were calculated and were correlated with the contents of phase2. The limit of the method is 0.3%. The sample after storage for 1 monthat 60° C. contains about 76% of the second crystal modificationaccording to this method.

EXAMPLE 4 Preparation of the Second Crystal Modification

Water-moist crude Leflunomide is first dissolved in isopropanol/water(corresponding to 16 kg of crude, dry Leflunomide in 28 I of isopropanolplus the amount of water which, together with the water content of themoist product, gives a total amount of water of 9 I).

The mixture is then heated to 78° C. to 82° C., stirred at thistemperature for 25 minutes (min) and then filtered through a pressurefunnel into a vessel also already heated to the same temperature. Thepressure filter is rinsed with an amount of isopropanol which, togetherwith isopropanol used (iPrOH), gives an iPrOH/water ratio of 4:1 (inthis case 4I). Thereafter, water also preheated to 78° C. to 82° C. isadded (32 I, gives iPrOH/water=0.8:1). The solution already becomescloudy and is then cooled to about 65° C. in 20 min, kept at thistemperature for about 40 min, then cooled to about 40° C. in 70 min andstirred for a further 20 min. The product is isolated by centrifuging.

Table 2 shows the results of 4 batches.

TABLE 2 Proportion* of Initial crystals of The concen- Final firstcrystal tration iPrOH/H₂O concentration modification Yield Batch [g/l]ratio [g/l] [%] [%] 1 600 4:1 600 n.d. 73.2 2 600 3:1 563 <0.4 71.4 3400 2:1 333 <0.4 70.5 4 400 0.8:1   222 <0.4 85.6 *The determination wascarried out by X-ray powder diffractometry; the proportion of the firstcrystal modification was always below the limit of detection, which wasabout 0.4 %. n.d. means not determined

The present invention may be embodied in other specific forms withoutdeparting from its spirit or essential characteristics. The describedembodiments are to be considered in all respects only as illustrativeand not restrictive. The scope of the invention is, therefore, indicatedby the appended claims rather than by the foregoing description. Allchanges which come within the meaning and range of equivalency of theclaims are to be embraced within their scope.

We claim:
 1. A method for detecting a first crystal modification of acompound of formula (I)

in a composition comprising the first crystal modification using X-raypowder diffraction.
 2. A method for quantifying the amount of a firstcrystal modification of a compound of formula (I)

in a composition comprising the first crystal modification.